1. Field of the Invention
The present invention relates to a pressure plate arrangement, and in particular for a motor vehicle friction clutch with automatic wear compensation. The pressure plate arrangement comprises a housing that can be connected fixedly to a flywheel and rotated with the flywheel about an axle. A pressure plate is connected to the housing in a substantially rotation-proof manner that is axially displaceable in the housing between an engagement position and a disengagement position. An energy storage device such as a diaphragm spring is operatively connected between the pressure plate and the housing. The energy storage device is supported by the housing in the axial direction. At the same time, the energy storage device is supported by the pressure plate via a wear compensation device and prestresses the pressure plate, relative to the housing, into the engagement position. In the engagement position, the pressure plate is preferably supported by the flywheel via friction linings of a clutch disk. The pressure plate arrangement further comprises at least one clearance indicator, which is arranged on the pressure plate. The clearance indicator has a wear detection section for detecting wear of the friction linings. Moreover, the clearance indicator includes a wear compensation section that interacts with the wear compensation device in order to compensate for the detected wear. In addition, the clearance indicator has a clamping seat section, by which the clearance indicator is held by the friction clamping seat on the pressure plate. When wear is detected by the wear detection section, the friction clamping seat may be substantially neutralized and the clearance indicator may be shifted, relative to the pressure plate, based on the amount of detected wear.
2. Description of the Related Art
A pressure plate arrangement is disclosed, for example, in German Patent Publication 295 07 449 U1. In this known pressure plate arrangement, the clearance indicator includes a bolt that extends substantially in the axial direction and penetrates a boring located radially outside of the pressure plate. For the purpose of detecting wear, a free end section of the bolt can be brought to rest on the flywheel of a clutch that is equipped with this pressure plate arrangement. A lever section located at the other end of the bolt rests, with its radially inner end, on the wear compensation device, so that the latter is blocked in the axial direction by the wear compensation section formed by the lever section. Arranged between the bolt of the clearance indicator and the radially inner end of the lever section is a second bolt, which extends axially from the pressure plate and penetrates an opening in the lever section. The clearance indicator is prestressed in a friction clamp seating on the pressure plate by means of two helical compression springs. A first helical compression spring acts between the free end of the bolt that penetrates the pressure plate and the pressure plate itself. A second helical compression spring acts further inward radially between the pressure plate and the lever section, and surrounds the second bolt located on the pressure plate. The spring action produces a tilting moment, which causes the bolt that penetrates the pressure plate to tilt in its opening, where it is fixed in place by means of friction clamping. When wear occurs, the clearance indicator is shifted out of its friction clamping seat against the spring force and moves in the axial direction accordingly based on the extent of detected wear. A subsequent disengagement movement, in which the wear compensation device is released by the diaphragm spring, allows this device to lengthen in the axial direction until it again comes to rest on the lever section.
A disadvantage associated with this type of pressure plate arrangement is that the bolt serving as the wear detection section and penetrating the pressure plate protrudes--in the case of pressure plate arrangements not composed of a flywheel and a clutch disk--over a base area of the pressure plate. This creates the risk that, during transport, an unintentional force will be exercised on the clearance indicator causing it to shift from the preassembled position into a position that corresponds to an operating position in which the clearance indicator has already detected wear. If such an unintentional movement goes unnoticed and the pressure plate arrangement is then assembled with a flywheel, the clearance indicator will not properly perform its wear-detecting function, at least not when the clutch begins operation.
Furthermore, such an unintentional movement of the clearance indicator also allows the wear compensation device to expand in the axial direction, so that later, when the pressure plate arrangement is assembled with a flywheel, the pressure plate has already moved too far toward the flywheel. Before assembling a clutch, it is therefore necessary to inspect all pressure plate arrangements of this type to determine whether any unintentional movement of the clearance indicator has taken place.
In addition, this conventional pressure plate arrangement is disadvantageous in that the clearance indicator, in order to detect the clearance relative to the flywheel, must penetrate the pressure plate with the bolt. The bolt section of the clearance indicator must therefore be arranged radially outside of the area where the clutch disk with the friction linings is positioned. It is not possible to move the bolt section radially inward because the clutch disk and its friction linings must be freely rotatable relative to the pressure plate and the flywheel. Furthermore, the structural size of this known pressure plate arrangement must be large enough for the bolt section of the clearance indicator to be arranged radially outside of the clutch disk in order to be connected to the pressure plate arrangement.